This section provides background information related to the present disclosure which is not necessarily prior art.
Reciprocating compressors typically include a compressor body housing a drive motor and one or more piston-cylinder arrangements. In operation, the drive motor imparts a force on each piston to move the pistons within and relative to respective cylinders. In so doing, a pressure of working fluid disposed within the cylinders is increased.
Conventional reciprocating compressors may be used in refrigeration systems such as heating, ventilation, and air conditioning systems (HVAC) to circulate a refrigerant amongst the various components of the refrigeration system. For example, a reciprocating compressor may receive suction-pressure, gaseous refrigerant from an evaporator and may elevate the pressure from suction pressure to discharge pressure. The discharge-pressure, gaseous refrigerant may exit the compressor and encounter a condenser to allow the refrigerant to change phase from a gas to a liquid. The liquid refrigerant may then be expanded via an expansion valve prior to returning to the evaporator where the cycle begins anew.
In the foregoing refrigeration system, the compressor requires electricity in order to drive the motor and compress refrigerant within the system from suction pressure to discharge pressure. As such, the amount of energy consumed by the compressor directly impacts the costs associated with operating the refrigeration system. Conventional compressors are therefore typically controlled to minimize energy consumption while still providing sufficient discharge-pressure refrigerant to the system to satisfy a cooling and/or heating demand.
Compressor capacity and, thus, the energy consumed by a reciprocating compressor during operation may be controlled by employing so-called “blocked-suction modulation.” Controlling compressor capacity via blocked-suction modulation typically involves starving the compressor of suction-pressure, gaseous refrigerant at times when a low volume of discharge-pressure refrigerant is required by the refrigeration system and allowing suction-pressure, gaseous refrigerant to freely flow into the compressor at times when a high volume of discharge-pressure refrigerant is required by the refrigeration system. Generally speaking, a low volume of discharge-pressure refrigerant is required at times when the load experienced by the refrigeration system is reduced and a high volume of discharge-pressure refrigerant is required at times when the load experienced by the refrigeration system is increased.
Controlling a reciprocating compressor via blocked-suction modulation reduces the energy consumption of the compressor during operation by reducing the load on the compressor to approximately only that which is required to meet system demand. However, conventional reciprocating compressors do not typically include a fluid-injection system such as a vapor-injection system or a liquid-injection system. As a result, conventional reciprocating compressor capacity is typically limited to the gains experienced via implementation of blocked-suction modulation and/or via a variable-speed drive.